A small diameter telescope provides a larger image of the Sun or solar eclipse than binoculars, and a much shorter projection distance. To begin, place a low-power eyepiece in the instrument.
In the case of a refractor, you have the option of inserting a star-diagonal between the focuser and the eyepiece itself: This arrangement will project the image at right angle to the telescope. Don’t forget to cover your finder scope, or better yet, remove it completely.
How to project the image of the Sun or a solar eclipse
Here are the steps to successfully project an image of the Sun:
- Centre the Sun by moving the telescope until its shadow appears the smallest;
- Project the Sun’s image onto a white cardboard placed about 20 cm from the eyepiece;
- Focus the image using the telescope’s focussing knob.
Place the screen inside a box to reduce ambient light that could reach it. The Sun’s image will have improved contrast.
Some commercial telescopes come equipped with a projection screen and mounting bracket. These are practical but not essential.
Important note about the instrument aperture
The telescope’s aperture should not exceed 5 cm (2") to avoid overheating and damaging the eyepiece. If necessary, construct a diaphragm by covering the open end of the telescope with cardboard that has a 4 to 5 cm hole cut into it.
The dust caps of some instruments are already fitted with a small hole covered by a cap. These are ideal. Make sure the dust cap, or cardboard diaphragm, is securely taped in place to avoid accidental removal.